U.S. patent application number 16/482416 was filed with the patent office on 2019-11-21 for mixed powder for powder metallurgy, sintered body, and method for producing sintered body.
This patent application is currently assigned to JFE STEEL CORPORATION. The applicant listed for this patent is JFE STEEL CORPORATION. Invention is credited to Akio KOBAYASHI, Naomichi NAKAMURA.
Application Number | 20190351483 16/482416 |
Document ID | / |
Family ID | 63040395 |
Filed Date | 2019-11-21 |
United States Patent
Application |
20190351483 |
Kind Code |
A1 |
KOBAYASHI; Akio ; et
al. |
November 21, 2019 |
MIXED POWDER FOR POWDER METALLURGY, SINTERED BODY, AND METHOD FOR
PRODUCING SINTERED BODY
Abstract
Disclosed is a mixed powder for powder metallurgy including: (a)
an iron-based powder containing Si in an amount of 0 mass % to 0.2
mass % and Mn in an amount of 0 mass % to 0.4 mass %, with the
balance being Fe and inevitable impurities; and (b) an alloyed
steel powder containing Mo in an amount of 2.0 mass % to 21.0 mass
%, Si in an amount of 0 mass % to 0.2 mass %, and Mn in an amount
of 0 mass % to 0.4 mass %, with the balance being Fe and inevitable
impurities, wherein a ratio of (b) the alloyed steel powder to a
total of (a) the iron-based powder and (b) the alloyed steel powder
is from 50 mass % to 90 mass %, and a ratio of Mo to the total of
(a) the iron-based powder and (b) the alloyed steel powder is from
2.2 mass % to 6.2 mass %.
Inventors: |
KOBAYASHI; Akio;
(Chiyoda-ku, Tokyo, JP) ; NAKAMURA; Naomichi;
(Chiyoda-ku, Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JFE STEEL CORPORATION |
Chiyoda-ku, Tokyo |
|
JP |
|
|
Assignee: |
JFE STEEL CORPORATION
Chiyoda-ku Tokyo
JP
|
Family ID: |
63040395 |
Appl. No.: |
16/482416 |
Filed: |
December 13, 2017 |
PCT Filed: |
December 13, 2017 |
PCT NO: |
PCT/JP2017/044702 |
371 Date: |
July 31, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 1/0003 20130101;
C22C 1/0425 20130101; C22C 38/02 20130101; C22C 38/16 20130101;
C22C 1/0425 20130101; C22C 33/0207 20130101; B22F 3/10 20130101;
B22F 2998/10 20130101; C22C 33/0207 20130101; B22F 2998/10
20130101; C22C 1/045 20130101; C22C 38/04 20130101; B22F 1/0059
20130101; C22C 1/055 20130101; B22F 2998/10 20130101; B22F 1/0059
20130101; B22F 1/00 20130101; C22C 38/12 20130101; C22C 1/0425
20130101; C22C 1/055 20130101; B22F 3/10 20130101; B22F 1/0059
20130101; B22F 3/02 20130101; C22C 1/05 20130101; B22F 3/02
20130101; C22C 33/0207 20130101 |
International
Class: |
B22F 1/00 20060101
B22F001/00; C22C 33/02 20060101 C22C033/02; C22C 38/02 20060101
C22C038/02; C22C 38/04 20060101 C22C038/04; C22C 38/12 20060101
C22C038/12; C22C 38/16 20060101 C22C038/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2017 |
JP |
2017-017861 |
Claims
1. A mixed powder for powder metallurgy comprising: (a) an
iron-based powder containing Si in an amount of 0 mass % to 0.2
mass % and Mn in an amount of 0 mass % to 0.4 mass %, with the
balance being Fe and inevitable impurities; and (b) an alloyed
steel powder containing Mo in an amount of 2.0 mass % to 21.0 mass
%, Si in an amount of 0 mass % to 0.2 mass %, and Mn in an amount
of 0 mass % to 0.4 mass %, with the balance being Fe and inevitable
impurities, wherein a ratio of (b) the alloyed steel powder to a
total of (a) the iron-based powder and (b) the alloyed steel powder
is from 50 mass % to 90 mass %, and a ratio of Mo to the total of
(a) the iron-based powder and (b) the alloyed steel powder is from
2.2 mass % to 6.2 mass %.
2. The mixed powder for powder metallurgy according to claim 1,
further comprising: (c) a Cu powder; and (d) a graphite powder,
wherein a ratio of (c) the Cu powder to a total of (a) the
iron-based powder, (b) the alloyed steel powder, (c) the Cu powder,
and (d) the graphite powder is from 0.5 mass % to 4.0 mass %, and a
ratio of (d) the graphite powder to the total of (a) the iron-based
powder, (b) the alloyed steel powder, (c) the Cu powder, and (d)
the graphite powder is from 0.2 mass % to 1.0 mass %.
3. The mixed powder for powder metallurgy according to claim 2,
further comprising: (e) a lubricant, wherein a ratio of (e) the
lubricant to the total of (a) the iron-based powder, (b) the
alloyed steel powder, (c) the Cu powder, and (d) the graphite
powder is from 0.2 mass % to 1.5 mass %.
4. A sintered body obtainable by forming and sintering the mixed
powder for powder metallurgy as recited in claim 1.
5. A method for producing a sintered body, comprising subjecting
the mixed powder for powder metallurgy as recited in claim 1 to
forming and sintering to obtain a sintered body.
6. A sintered body obtainable by forming and sintering the mixed
powder for powder metallurgy as recited in claim 2.
7. A sintered body obtainable by forming and sintering the mixed
powder for powder metallurgy as recited in claim 3.
8. A method for producing a sintered body, comprising subjecting
the mixed powder for powder metallurgy as recited in claim 2 to
forming and sintering to obtain a sintered body.
9. A method for producing a sintered body, comprising subjecting
the mixed powder for powder metallurgy as recited in claim 3 to
forming and sintering to obtain a sintered body.
Description
BACKGROUND
[0001] The present disclosure relates to a mixed powder for powder
metallurgy, and more particularly to a mixed powder for powder
metallurgy having excellent compressibility. The present disclosure
also relates to a sintered body using the mixed powder for powder
metallurgy and a method for producing the sintered body.
BACKGROUND
[0002] Powder metallurgy technology is a method that can form parts
with complicated shapes into a shape very close to the product
shape (so-called near net shape molding) and enables manufacture
with high dimensional accuracy. According to powder metallurgy
technology, cutting costs can be significantly reduced. For this
reason, powder metallurgical products are used as various
mechanical structures and parts thereof in many fields.
[0003] Further, in recent years, to achieve miniaturization and
reduced weight of parts, an increase in the strength of powder
metallurgical products is strongly requested. In particular, there
is a strong request for increasing the strength of iron-based
press-formed products and iron-based powder sintered products.
[0004] In order to meet the demand for higher strength, it has been
practiced to add an alloying element having a quench hardenability
improving effect to iron-based powder. For example, (1) pre-alloyed
steel powder and (2) partially diffusion-alloyed steel powder are
known as powders to which alloying elements are added at the stage
of raw material powder.
[0005] The pre-alloyed steel powder (1) is a powder in which
alloying elements are completely alloyed in advance. By using this
pre-alloyed steel powder, segregation of alloying elements can be
completely prevented, and the structure of the sintered body
becomes uniform. As a result, the mechanical characteristics as a
press-formed product or a sintered product can be stabilized.
However, since complete alloying causes solid solution hardening
over the entire powder particles, the compressibility of the powder
is low, causing a problem that the forming density is difficult to
increase during press forming.
[0006] The partially diffusion-alloyed steel powder (2) is a powder
in which each alloying element powder is partially adhered and
diffused on the surface of pure iron powder or pre-alloyed steel
powder. The partially diffusion-alloyed steel powder is prepared by
mixing metal powder of alloying elements or its oxide with pure
iron powder or pre-alloyed steel powder, and heating under a
non-oxidizing or reducing atmosphere to provide diffusion bonding
of alloying element powder on the surface of the pure iron powder
or pre-alloyed steel powder. With the use of partially
diffusion-alloyed steel powder, the structure can be made
relatively uniform, the mechanical properties of the product can be
stabilized as in the case of using the pre-alloyed steel powder.
Furthermore, since the partially diffusion-alloyed steel powder has
a portion in its inside which contains no or a small amount of
alloying elements, it exhibits good compressibility during press
forming as compared to the pre-alloyed steel powder.
[0007] As a basic alloy component to be used for the above
pre-alloyed steel powder and partially diffusion-alloyed steel
powder, Mo having a quench hardenability improving effect is widely
used. In addition to Mo, for example, Mn, Cr, and Si are known as
alloying elements having a quench hardenability improving effect.
However, among these elements, Mo is relatively hard to oxidize and
thus makes production of alloyed steel powder easy. For example,
pre-alloyed steel powder can be easily produced by making a molten
steel to which Mo is added as an alloying element into a powder
with a water atomizing method and subjecting the powder to finish
reduction in a normal hydrogen atmosphere. Also, partially
diffusion-alloyed steel powder can be easily produced by mixing Mo
oxide with pure iron powder or alloyed steel powder and performing
finish reduction in a normal hydrogen atmosphere.
[0008] As described above, by adding Mo having a quench
hardenability improving effect, the formation of ferrite is
suppressed and bainite or martensite is generated during hardening
treatment, and transformation toughening of the matrix phase is
achieved. Furthermore, Mo distributes to the matrix phase to
achieve solid solution strengthening of the matrix phase, and forms
fine carbides in the matrix phase to achieve strengthening by
precipitation of the matrix phase. Mo also has the effect of
enhancing carburization because it has a good gas carburizing
property and is a non-intergranular-oxidation element.
[0009] Examples of alloyed steel powder using Mo are described in,
for example, JP4371003B (PTL 1) and JPH04-231404A (PTL 2).
[0010] PTL 1 proposes alloyed steel powder in which Mo is further
diffusion-bonded to the surface of a pre-alloyed steel powder
containing Mo as an alloying element.
[0011] PTL 2 proposes applying a twice-forming twice-sintering
method when using Mo pre-alloyed steel powder in order to further
increase the strength of the sintered body. In the twice-forming
twice-sintering method, alloyed steel powder is subjected to
forming and pre-sintering, followed by the subsequent forming and
main sintering.
CITATION LIST
Patent Literature
[0012] PTL 1: JP4371003B
[0013] PTL 2: JPH04-231404A
SUMMARY
Technical Problem
[0014] However, the demand for increasing the strength of
iron-based powder press-formed products and iron-based powder
sintered products is becoming increasingly strong, yet the methods
proposed in PTLs 1 and 2 can not fully meet the demand. The reason
is as follows.
[0015] One method for increasing the strength of iron-based powder
press-formed products and iron-based powder sintered products is
densification. By increasing the density, the rearrangement of iron
powder particles proceeds and the void volume ratio inside the
formed product decreases, and the area in which the iron powder
particles come in contact with each other increases. As a result,
iron-based powder press-formed products and iron-based powder
sintered products have improved mechanical properties such as
tensile strength, impact value, and fatigue strength. In order to
increase the density of an iron-based powder sintered product or an
iron-based powder press-formed product, the compressibility of the
alloyed steel powder, which is a raw material for press forming,
may be increased to easily increase the forming density.
[0016] Therefore, in PTL 1, partially diffusion-alloyed steel
powder is used. As described above, since the partially
diffusion-alloyed steel powder has a portion which does not contain
alloying elements or has a small amount of alloying elements inside
the particles (hereinafter referred to as a "low alloy portion"),
it is excellent in the compressibility at the time of press forming
compared with pre-alloyed steel powder. It is thought that the
compressibility can be further improved by increasing the
proportion of the low alloy portion. However, it is necessary to
diffusion-bond a certain amount of alloying elements in order to
make the characteristics such as quench hardenability within the
desired range. Therefore, the proportion of a low alloy portion can
not be increased beyond a certain level, and thus sufficient
compressibility can not be ensured.
[0017] Furthermore, even if the twice-forming twice-sintering
method of PTL 2 is applied to the partially diffusion-alloyed steel
powder of PTL 1, the diffusion of alloying elements proceeds in the
first sintering, the compressibility in the second forming is
insufficient, and sufficient compressibility can not be
obtained.
[0018] It would thus be helpful to provide a mixed powder for
powder metallurgy that has higher compressibility than conventional
partially diffusion-alloyed steel powder and can obtain high
forming density. It would thus also be helpful to provide a
sintered body using the mixed powder for powder metallurgy, and a
method for producing the same.
Solution to Problem
[0019] As a result of conducting studies to solve the above
problems, the inventors obtained the following findings.
[0020] In the partially diffusion-alloyed steel powder, the source
at which high compressibility is developed is a low alloy portion
existing inside the particles making up the partially
diffusion-alloyed steel powder, that is, a portion containing no
alloying element or a small amount of alloying elements. In the low
alloy portion, the solid solution strengthening effect exerted by
the alloying elements is small, and deformation is easy during
press forming. On the contrary, since the alloying elements are
diffusion-bonded to the surface of the particles, the concentration
of the alloying elements is high and deformation is difficult.
[0021] As described above, the partially diffusion-alloyed steel
powder has the property that the surface is not easily deformed and
the inside is easily deformed. By having such an internal structure
of particles, partially diffusion-alloyed steel powder is more
likely to undergo rearrangement of particles than pre-alloyed
powder, and thus the forming density tends to increase. However, as
can be seen from the actual state of forming alloyed steel powder,
in order to fill the gaps between the particles and rearrange the
particles, it is desirable that the surface of the particles,
rather than the inside, is able to be deformed according to the
shape of particles present in the periphery.
[0022] However, in any of the pre-alloyed steel powder and the
partially diffusion-alloyed steel powder, the surface of the
particles contains an alloy component, and the surface of the
particles can not have such a soft state as described above.
[0023] Therefore, the inventors conceived of using a mixture of an
iron-based powder not containing Mo and an alloyed steel powder
containing Mo, instead of softening the surface of particles. By
using a combination of an alloyed steel powder containing Mo and an
iron-based powder with low hardness containing no Mo, the
compressibility at the time of press forming is improved even in
the case of ordinary single forming, and also in the twice-forming
twice-sintering method, if the alloying elements diffuse during the
first sintering, portions not containing Mo remains sufficiently to
maintain high compressibility even in the second forming. However,
if the mix proportion of the iron-based powder not containing Mo is
too small, such effects become insufficient, and conversely, if it
is too large, the mechanical properties are deteriorated.
[0024] Based on the above findings, the present disclosure was
conceived as a result of various studies on conditions under which
both compressibility and mechanical properties can be compatible.
In detail, we provide the following:
[0025] 1. A mixed powder for powder metallurgy comprising: (a) an
iron-based powder containing (consisting of) Si in an amount of 0
mass % to 0.2 mass % and Mn in an amount of 0 mass % to 0.4 mass %,
with the balance being Fe and inevitable impurities; and (b) an
alloyed steel powder containing (consisting of) Mo in an amount of
2.0 mass % to 21.0 mass %, Si in an amount of 0 mass % to 0.2 mass
%, and Mn in an amount of 0 mass % to 0.4 mass %, with the balance
being Fe and inevitable impurities, wherein a ratio of (b) the
alloyed steel powder to a total of (a) the iron-based powder and
(b) the alloyed steel powder is from 50 mass % to 90 mass %, and a
ratio of Mo to the total of (a) the iron-based powder and (b) the
alloyed steel powder is from 2.2 mass % to 6.2 mass %.
[0026] 2. The mixed powder for powder metallurgy according to 1
above, further comprising: (c) a Cu powder; and (d) a graphite
powder, wherein a ratio of (c) the Cu powder to a total of (a) the
iron-based powder, (b) the alloyed steel powder, (c) the Cu powder,
and (d) the graphite powder is from 0.5 mass % to 4.0 mass %, and a
ratio of (d) the graphite powder to the total of (a) the iron-based
powder, (b) the alloyed steel powder, (c) the Cu powder, and (d)
the graphite powder is from 0.2 mass % to 1.0 mass %.
[0027] 3. The mixed powder for powder metallurgy according to 2
above, further comprising: (e) a lubricant, wherein a ratio of (e)
the lubricant to the total of (a) the iron-based powder, (b) the
alloyed steel powder, (c) the Cu powder, and (d) the graphite
powder is from 0.2 mass % to 1.5 mass %.
[0028] 4. A sintered body obtainable by forming and sintering the
mixed powder for powder metallurgy as recited in any one of 1 to 3
above.
[0029] 5. A method for producing a sintered body, comprising
subjecting the mixed powder for powder metallurgy as recited in any
one of 1 to 3 above to forming and sintering to obtain a sintered
body.
Advantageous Effect
[0030] The mixed powder for powder metallurgy disclosed herein is
superior in compressibility to the conventional partially
diffusion-alloyed steel powder, and it can be used not only in the
usual single-forming single-sintering method but also in the
twice-forming twice-sintering method to obtain a press-formed
product having a high forming density. Moreover, according to the
present disclosure, a sintered body having high strength can be
obtained.
DETAILED DESCRIPTION
[0031] The following describes the present disclosure in detail. In
the following description, "%" notation represents "mass %" unless
otherwise specified.
[0032] The mixed powder for powder metallurgy (hereinafter
sometimes simply referred to as "mixed powder") in one of the
embodiments disclosed herein contains, as essential components, (a)
an iron-based powder and (b) an alloyed steel powder.
[0033] (a) Iron-based Powder
As the iron-based powder, an iron-based metal powder containing Si
in an amount of 0% to 0.2% and Mn in an amount of 0% to 0.4%, with
the balance being Fe and inevitable impurities, is used. The
iron-based powder has an effect of securing the compressibility at
the time of press forming by being mixed with (b) the alloyed steel
powder. Therefore, it is desirable that the iron-based powder be as
soft as possible. If the iron-based powder contains an element
other than Fe, the compressibility decreases. Therefore, an iron
powder composed of Fe and inevitable impurities (also referred to
as "pure iron powder") is preferably used as the iron-based
powder.
[0034] Note that Si and Mn are contained as impurities in general
iron-based powder. Si and Mn are elements having the effect of
improving the quench hardenability in addition to the effect of
increasing the strength by solid solution strengthening. Therefore,
when Si and Mn are contained, the strength of the sintered body may
be improved depending on the cooling conditions at the time of
sintering the press-formed product and the conditions such as
quenching and tempering conditions, and hence these elements may
work advantageously in reverse. From the above reasons, the
iron-based powder is permitted to contain one or both of Si and Mn
in the range described below.
[0035] Si: 0% to 0.2%
Si is an element having the effect of increasing the strength of
steel by quench hardenability improvement, solid solution
strengthening, and the like. However, when the Si content in the
iron-based powder exceeds 0.2%, more oxides form and the
compressibility decreases, and the oxides become the starting point
of fracture in the sintered body, causing the fatigue strength and
toughness to decrease. Therefore, the Si content of the iron-based
powder is 0.2% or less. On the other hand, as described above, from
the viewpoint of compressibility, a lower Si content is preferable.
Thus, the Si content may be 0%. Therefore, the Si content of the
iron-based powder is 0% or more.
[0036] Mn: 0% to 0.4%
Mn, like Si, is also an element having the effect of increasing the
strength of steel by quench hardenability improvement, solid
solution strengthening, and the like. However, when the Mn content
in the iron-based powder exceeds 0.4%, more oxides form and the
compressibility decreases, and the oxides become the starting point
of fracture in the sintered body, causing the fatigue strength and
toughness to decrease. Therefore, the Mn content of the iron-based
powder is 0.4% or less. On the other hand, as described above, from
the viewpoint of compressibility, a lower Mn content is preferable.
Thus, the Mn content may be 0%. Therefore, the Mn content of the
iron-based powder is 0% or more.
[0037] Although the amount of inevitable impurities contained in
the iron-based powder is not particularly limited, the total amount
is preferably 1.0 mass % or less, more preferably 0.5 mass % or
less, and even more preferably 0.3 mass % or less. Among the
elements contained as inevitable impurities, the P content is
preferably 0.020% or less. The S content is preferably 0.010% or
less. The O content is preferably 0.20% or less. The N content is
preferably 0.0015% or less. The Al content is preferably 0.001% or
less. The Mo content is preferably 0.010% or less.
[0038] (b) Alloyed Steel Powder
As the above alloyed steel powder, an alloyed steel powder
containing Mo in an amount of 2.0% to 21.0%, Si in an amount of 0%
to 0.2%, and Mn in an amount of 0% to 0.4%, with the balance being
Fe and inevitable impurities, is used. The alloyed steel powder has
a role of supplying Mo, which is an alloying element. By using a
mixture of (b) the alloyed steel powder containing Mo and (a) the
iron-based powder containing no Mo, both excellent powder
compressibility and high mechanical strength of the sintered body
can be achieved at a high level.
[0039] Mo: 2.0% to 21.0%
[0040] As mentioned above, since Mo is difficult to oxidize and to
be reduced to the same degree as Fe, an alloyed steel powder
containing Mo can be produced relatively easily. In addition to the
function of transformation strengthening of the matrix phase during
quenching by the quench hardenability improving effect, Mo acts to
achieve solid solution strengthening of the matrix phase when
distributed to the matrix phase and strengthening by precipitation
of the matrix phase by forming fine carbides in the matrix phase.
Mo also has the effect of enhancing carburization because it has a
good gas carburizing property and is a non-intergranular-oxidation
element. Therefore, Mo is very useful as a strengthening
element.
[0041] However, in the present disclosure, since the iron-based
powder and the alloyed steel powder are mixed and used, the Mo
content of the whole mixed powder for powder metallurgy is lower
than that of the original alloyed steel powder. For example, when
the mixed powder for powder metallurgy consists only of iron-based
powder and alloying powder, the percentage of the alloyed steel
powder is 50% to 90% as described later, the Mo content of the
whole mixed powder is 1/2 to 9/10 of that in the alloyed steel
powder. In consideration of this, the Mo content of the alloyed
steel powder is 2.0% or more. If the Mo content is less than 2.0%,
the above-described effect of Mo as a strengthening element can not
be sufficiently obtained. On the other hand, when the Mo content of
the alloyed steel powder exceeds 21.0%, the toughness is lowered.
Therefore, the Mo content of the alloyed steel powder is 21.0% or
less.
[0042] Since alloying elements other than Mo are basically not
used, the balance other than Mo of the alloyed steel powder may be
Fe and inevitable impurities. Note that general alloyed steel
powder contains Si and Mn as impurities. As described above, Si and
Mn are elements having the effect of improving the hardenability in
addition to the effect of improving the strength by solid solution
strengthening. Therefore, when Si and Mn are contained, the
strength of the sintered body may be improved depending on the
cooling conditions at the time of sintering the press-formed
product and the conditions such as quenching and tempering
conditions, and hence these elements may work advantageously in
reverse. For the above reasons, the alloyed steel powder is
permitted to contain one or both of Si and Mn in the range
described below.
[0043] Si: 0% to 0.2%
Si is an element having the effect of increasing the strength of
steel by quench hardenability improvement, solid solution
strengthening, and the like. However, when the Si content in the
alloyed steel powder exceeds 0.2%, the formation of oxides
increases and the compressibility decreases, and the oxides become
the starting point of fracture in the sintered body, causing the
fatigue strength and toughness to decrease. Therefore, the Si
content of the alloyed steel powder is 0.2% or less. On the other
hand, as mentioned above, from the viewpoint of compressibility, a
lower Si content is preferable. Thus, the Si content may be 0%.
Therefore, the Si content of the alloyed steel powder is 0% or
more.
[0044] Mn: 0% to 0.4%
Mn, like Si, is also an element having the effect of increasing the
strength of steel by hardenability improvement, solid solution
strengthening, and the like. However, when the Mn content in the
alloyed steel powder exceeds 0.4%, more oxides form and the
compressibility decreases, and the oxides become the starting point
of fracture in the sintered body, causing the fatigue strength and
toughness to decrease. Therefore, the Mn content of the alloyed
steel powder is 0.4% or less. On the other hand, as described
above, from the viewpoint of compressibility, a lower Mn content is
preferable. Thus, the Mn content may be 0%. Therefore, the Mn
content of the alloyed steel powder is 0% or more.
[0045] Although the amount of inevitable impurities contained in
the above alloyed steel powder is not particularly limited, the
total amount is preferably 1.0 mass % or less, more preferably 0.5
mass % or less, and even more preferably 0.3 mass % or less. Among
the elements contained as inevitable impurities, the P content is
preferably 0.020% or less. The S content is preferably 0.010% or
less. The O content is preferably 0.20% or less. The N content is
preferably 0.0015% or less. The Al content is preferably 0.001% or
less.
[0046] The alloyed steel powder is not particularly limited, and
any powder may be used as long as it has the above-described
chemical composition. For example, the alloyed steel powder may be
one or both of a pre-alloyed steel powder and a partially
diffusion-alloyed steel powder. In addition, as the partially
diffusion-alloyed steel powder, one or both of an iron powder (pure
iron powder) with an alloying element diffusion-bonded to the
surface thereof, and a pre-alloyed steel powder with an alloying
element diffused and attached on the surface thereof.
[0047] Ratio of the Alloyed Steel Powder: 50% to 90%
The ratio of the mass of (b) the alloyed steel powder to the total
mass of (a) the iron-based powder and (b) the alloyed steel powder
(hereinafter simply referred to as "the ratio of the alloyed steel
powder") is from 50% to 90%. When the ratio of the alloyed steel
powder is less than 50%, that is, the ratio of the iron-based
powder exceeds 50%, the portions of the iron-based powder having
low strength are connected inside the sintered body, and when the
sintered body is stressed, a crack develops in portions having
lower strength, which tends to lead to a fracture. Therefore, the
ratio of the alloyed steel powder is 50% or more. On the other
hand, when the ratio of the alloyed steel powder exceeds 90%, that
is, the ratio of the iron-based powder is less than 10%, the soft
portions contributing to the compressibility decrease, and the
compressibility of the whole mixed powder is insufficient.
Therefore, the ratio of the alloyed steel powder is 90% or
less.
[0048] Ratio of Mo: 2.2% to 6.2%
When the ratio of the mass of Mo to the total mass of (a) the
iron-based powder and (b) the alloyed steel powder (hereinafter
simply referred to as "the ratio of Mo") is less than 2.2%, the
effect of Mo as an strengthening element is insufficient.
Therefore, the ratio of Mo is 2.2% or more. On the other hand, the
excessive addition of Mo causes an increase in alloy cost, the
ratio of Mo is 6.2% or less.
[0049] The mixed powder for powder metallurgy in one of the
embodiments disclosed herein may be made of (a) the iron-based
powder and (b) the alloyed steel powder only (iron-based
powder+alloyed steel powder=100%), it may also contain any other
component(s). However, if the ratio of the total mass of (a) the
iron-based powder and (b) the alloyed steel powder to the mass of
the mixed powder as a whole is excessively low, the mechanical
properties of the sintered body are degraded. Therefore, the ratio
of the total mass of (a) the iron-based powder and (b) the alloyed
steel powder to the mass of the mixed powder as a whole is
preferably 90% or more, and preferably 95% or more.
[0050] In one of the disclosed embodiments, (c) Cu powder and (d)
graphite powder may be further added to the mixed powder for powder
metallurgy. By adding Cu powder and graphite powder, the strength
of the sintered body can be further improved.
[0051] (c) Cu Powder
Cu is an element that promotes the solid solution strengthening and
the quench hardenability improvement of the iron-based powder and
has the effect of increasing the strength of the sintered body. If
the addition amount of the Cu powder is less than 0.5%, the
above-described effect can not be sufficiently obtained. Therefore,
when used, the addition amount of the Cu powder is 0.5% or more.
The addition amount of the Cu powder is preferably 1.0% or more. On
the other hand, when the addition amount of the Cu powder exceeds
4.0%, not only the strength improving effect of the sintered parts
is saturated, but rather the sintering density is lowered.
Therefore, the addition amount of the Cu powder is 4.0% or less.
The addition amount of the Cu powder is preferably 3.0% or less. As
used herein, "the addition amount of the Cu powder" means the ratio
of the mass of (c) the Cu powder to the total mass of (a) the
iron-based powder, (b) the alloyed steel powder, (c) the Cu powder,
and (d) the graphite powder.
[0052] (d) Graphite Powder
Graphite is an effective component to increase the strength. If the
addition amount of the graphite powder is less than 0.2%, the above
effect can not be sufficiently obtained. Therefore, when used, the
addition amount of the graphite powder is 0.2% or more. The
addition amount of the graphite powder is preferably 0.3% or more.
On the other hand, when the addition amount of the graphite powder
exceeds 1.0%, the precipitation amount of cementite due to
hypereutectoid increases to cause a decrease in strength.
Therefore, the addition amount of the graphite powder is 1.0% or
less. The addition amount of the graphite powder is preferably 0.8%
or less. As used herein, "the addition amount of the graphite
powder" refers to the ratio of the mass of (d) the graphite powder
to the total mass of (a) the iron-based powder, (b) the alloyed
steel powder, (c) the Cu powder, and (d) the graphite powder.
[0053] In one of the disclosed embodiments, (e) a lubricant can be
further added to the mixed powder for powder metallurgy. By adding
the lubricant, it is possible to suppress the wear at the time of
pressing of the mixed powder for powder metallurgy to extend the
life of the mold and to further increase the density of the formed
body.
[0054] (e) Lubricant
If the addition amount of the lubricant is less than 0.2%, the
above effect is hardly exhibited. Therefore, when used, the
addition amount of the lubricant is 0.2% or more. The addition
amount of the lubricant is preferably 0.3% or more. On the other
hand, when the addition amount of the lubricant exceeds 1.5%, the
non-metal part in the mixed powder increases and the forming
density becomes difficult to increase, causing the strength to
decrease. Therefore, the addition amount of the lubricant is 1.5%
or less. The addition amount of the lubricant is preferably 1.2% or
less. As used herein, "the addition amount of the lubricant" means
the ratio of the mass of (e) the lubricant to the total mass of (a)
the iron-based powder, (b) the alloyed steel powder, (c) the Cu
powder, and (d) the graphite powder.
[0055] The lubricant is not particularly limited and may be of any
type. As the lubricant, for example, one or more selected from the
group consisting of fatty acids, fatty acid amides, fatty acid
bisamides, and metal soaps can be used. Among them, metal soaps
such as lithium stearate and zinc stearate, or amide-based
lubricants such as ethylene bis stearoamide are preferably
used.
[0056] In addition to the method for adding and mixing a lubricant
to the mixed powder, a method for directly applying a lubricant to
a mold can also be used, and a method for combining both can also
be used.
[0057] In one of the disclosed embodiments, a sintered body can be
produced using the above-described mixed powder for powder
metallurgy. The method for producing the sintered body is not
particularly limited, and may be produced by any method. However,
usually, the mixed powder for powder metallurgy may be pressed and
formed into a formed body according to a conventional method in
powder metallurgy, and then sintered.
[0058] The density of the formed body (sometimes referred to as the
"forming density") is not particularly limited, yet from the
viewpoint of securing sufficient mechanical properties (such as
toughness), it is preferably 6.85 Mg/m.sup.3 or more. Moreover,
although the tensile strength required for the sintered body varies
with the uses and the like, it is preferable that the sintered body
have a tensile strength of 620 MPa or more.
EXAMPLES
Example 1
[0059] Mixed powders for powder metallurgy were produced using an
iron-based powder containing Si and Mn only as inevitable
impurities and an alloyed steel powder, and the performance was
evaluated. The specific steps were as follows.
[0060] (a) The iron-based powder was produced by subjecting the
iron powder produced by the water atomization method to a finish
reduction treatment at 900.degree. C. for 60 minutes in hydrogen
atmosphere for decarburization and deoxidation, and subjecting the
obtained cake to a crushing treatment. The chemical compositions of
the obtained iron-based powders are listed in Table 1. Note that
the elements illustrated in Table 1 are all contained as inevitable
impurities in the iron-based powder.
[0061] (b) As the alloyed steel powder, two different powders,
i.e., a pre-alloyed steel powder and a composite alloyed steel
powder were used. The pre-alloyed steel powder was produced by the
same method as the above-described iron-based powder except that
one containing Mo was used as the molten metal to be subjected to
water atomization. As a result, the alloyed steel powder was
obtained in which all of Mo as an alloying element was added as a
pre-alloy. The chemical compositions of the obtained pre-alloyed
steel powders are listed in Table 1.
[0062] The composite alloyed steel powder was produced by producing
a pre-alloyed steel powder containing 5.0 mass % of Mo with the
same method as the above pre-alloyed steel powder, and further
diffusion-bonding Mo on the surface of the obtained pre-alloyed
steel powder. In the diffusion-bonding process, the pre-alloyed
steel powder was mixed with MoO.sub.3 powder in an amount
equivalent to the Mo content of 1.0 mass %, 1.7 mass %, 3.6 mass %,
7.0 mass %, and 15.0 mass %, respectively, and the mixture was
subjected to a heat treatment in hydrogen atmosphere at 900.degree.
C. for 60 minutes. By the heat treatment, the pre-alloyed steel
powder was decarburized and deoxidized, and at the same time, Mo
generated by reduction of MoO.sub.3 was diffusion-bonded to the
pre-alloyed steel powder. By crushing the cake obtained by the
above-described treatment, a composite alloyed steel powder in
which Mo was diffusion-bonded to the surface of the pre-alloyed
steel powder was obtained. The chemical compositions of the
obtained composite alloyed steel powders are also listed in Table
1.
[0063] Next, (a) the iron-based powder and (b) the alloyed steel
powder thus obtained were mixed in a V-type mixer for 15 minutes in
the combination and ratio listed in Table 2 to obtain a mixed
powder of iron-based powder and alloyed steel powder. The mixing
ratio of (a) the iron-based powder and (b) the alloyed steel powder
was selected intending that the ratio of Mo to the total of (a) the
iron-based powder and (b) the alloyed steel powder be 2.3 mass % or
6.0 mass %, and the calculated values of the ratio of Mo are also
listed in Table 2.
[0064] Then, Cu powder, graphite powder, and Wax-based lubricant
powder were further added to each mixed powder of iron base powder
and alloyed steel powder in the proportions listed in Table 2 and
mixed in a V-type mixer for 15 minutes to obtain a mixed powder for
powder metallurgy. In Nos. 1 to 3, only the lubricant was added
without using the Cu powder and the graphite powder.
[0065] The properties of the obtained mixed powder for powder
metallurgy were evaluated in the following procedure.
Density of Press-Formed Body
[0066] Using the mixed powders for powder metallurgy, press-formed
bodies were produced as test pieces, and their densities were
evaluated, respectively. Each press-formed body was in the form of
a ring having an outer diameter of 38 mm.PHI., an inner diameter of
25 mm.PHI., and a height of 10 mm, and the forming pressure was 686
MPa. The weight of the obtained formed body was measured, and the
density was determined by dividing the measured weight by the
volume calculated from the dimensions. The results are as listed in
Table 2.
Tensile Strength of Sintered Body
[0067] As a tension test piece, a sintered body was fabricated from
each mixed powder for powder metallurgy, and the tensile strength
was measured. The tensile test piece was produced by forming a
mixed powder for powder metallurgy into a tensile test piece having
a parallel part of 5.8 mm wide and 5 mm high, and performing
sintering for 20 minutes at 1130.degree. C. in RX gas atmosphere.
The results are listed in Table 2.
[0068] From the results in Table 2, it can be seen that as the
mixing ratio of the iron-based powder increases, the forming
density increases, and the tensile strength tends to increase and
then decrease. In each example satisfying the conditions according
to the present disclosure, the forming density of 6.85 Mg/m.sup.3
or more and the tensile strength of 620 MPa or more were obtained.
In contrast, in each case where the mixing ratio of the iron-based
powder was 0 mass %, when the Mo content of the mixed powder was
2.3 mass %, the tensile strength did not reach 620 MPa, and when
the Mo content of the mixed powder was 6.0 mass %, the forming
density did not reach 6.85 Mg/m.sup.3 and the tensile strength did
not reach 620 MPa. In addition, in each case where the mixing ratio
of the pure iron powder was 70 mass % or more, the tensile strength
did not reach 620 MPa when the Mo content of the mixed powder was
2.3 mass % or 6.0 mass %.
TABLE-US-00001 TABLE 1 Chemical composition (mass %)* Type ID Type
of alloyed steel powder C Si Mn P S O N Al Mo (a) Iron-based a-1 --
0.003 0.012 0.02 0.009 0.005 0.18 0.0009 <0.001 0.004 powder a-2
-- 0.003 0.013 0.03 0.011 0.006 0.16 0.0010 <0.001 0.005 (b)
Alloyed b-01 pre-alloyed steel powder 0.002 0.013 0.04 0.013 0.007
0.16 0.0007 <0.001 2.3 steel powder b-02 pre-alloyed steel
powder 0.003 0.013 0.04 0.014 0.004 0.16 0.0007 <0.001 2.5 b-03
pre-alloyed steel powder 0.002 0.014 0.04 0.013 0.004 0.16 0.0006
<0.001 3.3 b-04 pre-alloyed steel powder 0.002 0.013 0.03 0.013
0.005 0.16 0.0006 <0.001 4.7 b-05 pre-alloyed steel powder 0.003
0.014 0.03 0.012 0.005 0.16 0.0006 <0.001 7.9 b-11 composite
alloyed steel powder 0.004 0.014 0.04 0.014 0.007 0.17 0.0007
<0.001 5.9 b-12 composite alloyed steel powder 0.003 0.015 0.04
0.014 0.007 0.17 0.0007 <0.001 6.9 b-13 composite alloyed steel
powder 0.003 0.016 0.04 0.016 0.005 0.18 0.0008 <0.001 8.8 b-14
composite alloyed steel powder 0.003 0.016 0.05 0.016 0.005 0.18
0.0007 <0.001 12.2 b-15 composite alloyed steel powder 0.002
0.015 0.04 0.015 0.006 0.17 0.0007 <0.001 20.5 *The balance is
Fe and other inevitable impurities.
TABLE-US-00002 TABLE 2 Formulation of mixed powder for powder
metallurgy Evaluation result (a) Iron-based (b) Alloyed steel (c)
Cu (d) Graphite (e) Tensile powder powder powder powder Lubricant
Density strength Addition Addition Additon Additon Additon of of
amount amount Ratio amount amount amount fomed sintered *1 *1 of Mo
*1 *2 *2 *2 body body No. Type (mass %) Type (mass %) (mass %)
(mass %) (mass %) (mass %) (Mg/m.sup.3) (MPa) Category 1 a-1 0 b-01
100 2.3 -- -- 0.5 6.91 585 Comparative example 2 30 b-03 70 2.3 --
-- 0.5 7.04 633 Example 3 70 b-05 30 2.4 -- -- 0.5 7.18 491
Comparative example 4 a-1 0 b-01 100 2.3 2.0 0.7 0.5 6.89 596
Comparative example 5 10 b-02 90 2.3 2.0 0.7 0.5 6.99 628 Example 6
30 b-03 70 2.3 2.0 0.7 0.5 7.06 642 Example 7 50 b-04 50 2.4 2.0
0.7 0.5 7.11 628 Example 8 70 b-05 30 2.4 2.0 0.7 0.5 7.16 504
Comparative example 9 a-2 0 b-11 100 5.9 2.0 0.7 0.5 6.83 616
Comparative example 10 10 b-12 90 6.2 2.0 0.7 0.5 6.88 638 Example
11 30 b-13 70 6.2 2.0 0.7 0.5 6.95 657 Example 12 50 b-14 50 6.1
2.0 0.7 0.5 7.01 646 Example 13 70 b-15 30 6.2 2.0 0.7 0.5 7.09 543
Comparative example *1: Ratio to the total of (a) iron-based powder
and (b) alloyed steel powder. *2: Ratio to the total of (a)
iron-based powder, (b) alloyed steel powder, (c) Cu powder, and (d)
graphite powder.
Example 2
[0069] Mixed powders for powder metallurgy were produced in the
same manner as in Example 1 except that an iron-based powder
containing Mn and an alloyed steel powder were used, and the
performance was evaluated. Table 3 lists the compositions of the
iron-based powder and alloyed steel powder used, and Table 4 lists
the blending ratio of each component and the evaluation
results.
[0070] As can be seen from the results in Table 4, as in the case
of Example 1, as the mixing ratio of the iron-based powder
increases, the forming density increases, and the tensile strength
once increases and then decreases. In addition, in each example
satisfying the conditions according to the present disclosure, the
forming density of 6.85 Mg/m.sup.3 or more and the tensile strength
of 620 MPa or more were obtained.
TABLE-US-00003 TABLE 3 Chemical composition (mass %)* Type ID Type
of alloyed steel powder C Si Mn P S O N Al Mo (a) Iron-based a-3 --
0.004 0.014 0.20 0.013 0.005 0.17 0.0006 <0.001 0.005 powder a-4
-- 0.003 0.016 0.16 0.011 0.004 0.16 0.0007 <0.001 0.003 (b)
Alloyed b-21 pre-alloyed steel powder 0.004 0.015 0.22 0.013 0.005
0.18 0.0006 <0.001 2.3 steel powder b-22 pre-alloyed steel
powder 0.004 0.016 0.23 0.012 0.005 0.18 0.0007 <0.001 2.6 b-23
pre-alloyed steel powder 0.003 0.016 0.22 0.013 0.006 0.18 0.0006
<0.001 3.4 b-24 pre-alloyed steel powder 0.003 0.017 0.23 0.013
0.006 0.18 0.0007 <0.001 4.4 b-25 pre-alloyed steel powder 0.004
0.016 0.22 0.013 0.005 0.17 0.0006 <0.001 8.0 b-31 composite
alloyed steel powder 0.003 0.011 0.18 0.013 0.005 0.17 0.0006
<0.001 2.4 b-32 composite alloyed steel powder 0.003 0.012 0.18
0.013 0.006 0.16 0.0005 <0.001 2.7 b-33 composite alloyed steel
powder 0.004 0.013 0.17 0.013 0.005 0.16 0.0005 <0.001 3.5 b-34
composite alloyed steel powder 0.005 0.012 0.18 0.014 0.005 0.16
0.0005 <0.001 4.3 b-35 composite alloyed steel powder 0.005
0.012 0.17 0.014 0.006 0.16 0.0005 <0.001 7.8 b-41 pre-alloyed
steel powder 0.004 0.015 0.19 0.016 0.005 0.16 0.0004 <0.001 3.5
b-42 pre-alloyed steel powder 0.004 0.015 0.20 0.016 0.006 0.16
0.0003 <0.001 3.9 b-43 pre-alloyed steel powder 0.005 0.015 0.21
0.015 0.005 0.16 0.0004 <0.001 5.1 b-44 pre-alloyed steel powder
0.005 0.014 0.20 0.015 0.005 0.16 0.0004 <0.001 6.9 b-45
pre-alloyed steel powder 0.005 0.014 0.21 0.015 0.005 0.16 0.0004
<0.001 11.4 b-51 pre-alloyed steel powder 0.002 0.011 0.23 0.013
0.005 0.18 0.0007 <0.001 5.0 b-52 pre-alloyed steel powder 0.003
0.010 0.24 0.014 0.005 0.17 0.0007 <0.001 5.4 b-53 pre-alloyed
steel powder 0.002 0.011 0.23 0.015 0.006 0.16 0.0007 <0.001 7.3
b-54 pre-alloyed steel powder 0.003 0.011 0.23 0.015 0.006 0.17
0.0006 <0.001 9.8 b-55 pre-alloyed steel powder 0.003 0.012 0.22
0.014 0.005 0.17 0.0005 <0.001 17.0 b-61 composite alloyed steel
powder 0.004 0.017 0.22 0.014 0.003 0.16 0.0005 <0.001 6.1 b-62
composite alloyed steel powder 0.004 0.015 0.23 0.015 0.003 0.16
0.0005 <0.001 6.7 b-63 composite alloyed steel powder 0.004
0.016 0.23 0.015 0.004 0.16 0.0006 <0.001 8.5 b-64 composite
alloyed steel powder 0.005 0.017 0.23 0.015 0.002 0.16 0.0006
<0.001 12.4 b-65 composite alloyed steel powder 0.004 0.016 0.22
0.015 0.003 0.16 0.0005 <0.001 19.9 *The balance is Fe and other
inevitable impurities.
TABLE-US-00004 TABLE 4 Formulation of mixed powder for powder
metallurgy Evaluation result (a) Iron-based (b) Alloyed steel (c)
Cu (d) Graphite (e) Tensile powder powder powder powder Lubricant
Density strength Additon Additon Additon Additon Additon of of
amount amount Ratio amount amount amount fomed sintered *1 *1 of Mo
*1 *2 *2 *2 body body No. Type (mass %) Type (mass %) (mass %)
(mass %) (mass %) (mass %) (Mg/m.sup.3) (MPa) Category 14 a-3 0
b-21 100 2.3 2.0 0.7 0.5 6.87 602 Comparative example 15 10 b-22 90
2.3 2.0 0.7 0.5 6.97 634 Example 16 30 b-23 70 2.4 2.0 0.7 0.5 7.05
653 Example 17 50 b-24 50 2.2 2.0 0.7 0.5 7.08 635 Example 18 70
b-25 30 2.4 2.0 0.7 0.5 7.15 522 Comparative example 19 a-4 0 b-31
100 2.4 2.0 0.7 0.5 6.88 608 Comparative example 20 10 b-32 90 2.4
2.0 0.7 0.5 6.98 641 Example 21 30 b-33 70 2.5 2.0 0.7 0.5 7.07 659
Example 22 50 b-34 50 2.2 2.0 0.7 0.5 7.11 648 Example 23 70 b-35
30 2.3 2.0 0.7 0.5 7.17 529 Comparative example 24 a-3 0 b-41 100
3.5 2.0 0.7 0.5 6.85 613 Comparative example 25 10 b-42 90 3.5 2.0
0.7 0.5 6.94 648 Example 26 30 b-43 70 3.6 2.0 0.7 0.5 7.03 665
Example 27 50 b-44 50 3.5 2.0 0.7 0.5 7.09 654 Example 28 70 b-45
30 3.4 2.0 0.7 0.5 7.14 539 Comparative example 29 a-4 0 b-51 100
5.0 2.0 0.7 0.5 6.83 616 Comparative example 30 10 b-52 90 4.9 2.0
0.7 0.5 6.89 646 Example 31 30 b-53 70 5.1 2.0 0.7 0.5 6.97 661
Example 32 50 b-54 50 4.9 2.0 0.7 0.5 7.03 658 Example 33 70 b-55
30 5.1 2.0 0.7 0.5 7.10 542 Comparative example 34 a-4 0 b-61 100
6.1 2.0 0.7 0.5 6.82 623 Comparative example 35 10 b-62 90 6.0 2.0
0.7 0.5 6.86 643 Example 36 30 b-63 70 6.0 2.0 0.7 0.5 6.94 664
Example 37 50 b-64 50 6.2 2.0 0.7 0.5 7.00 656 Example 38 70 b-65
30 6.0 2.0 0.7 0.5 7.08 549 Comparative example *1: Ratio to the
total of (a) iron-based powder and (b) alloyed steel powder. *2:
Ratio to the total of (a) iron-based powder, (b) alloyed steel
powder, (c) Cu powder, and (d) graphite powder.
Example 3
[0071] Mixed powders for powder metallurgy were produced in the
same manner as in Example 1 except that an iron-based powder
containing Si and Mn and an alloyed steel powder were used, and the
performance was evaluated. Table 5 lists the compositions of the
iron-based powder and alloyed steel powder used, and Table 6 lists
the blending ratio of each component and the evaluation
results.
[0072] As can be seen from the results in Table 6, as in the case
of Examples 1 and 2, as the mixing ratio of the iron-based powder
increases, the forming density increases, and the tensile strength
once increases and then decreases. In addition, in each example
satisfying the conditions according to the present disclosure, the
forming density of 6.85 Mg/m.sup.3 or more and the tensile strength
of 620 MPa or more were obtained. Further, in Examples 2 and 3
using the raw material powder containing one or both of Si and Mn,
it can be seen that the tensile strength of the sintered body was
improved compared to Example 1 while maintaining the high density
of the sintered body. From this follows that it is preferable to
add one or both of Si and Mn when importance is attached to
strength.
TABLE-US-00005 TABLE 5 Chemical composition (mass %)* Type ID Type
of alloyed steel powder C Si Mn P S O N Al Mo (a) Iron-based a-5 --
0.003 0.21 0.40 0.012 0.006 0.16 0.0004 <0.001 0.006 powder a-6
-- 0.004 0.20 0.39 0.013 0.005 0.16 0.0006 <0.001 0.005 (b)
Alloyed b-71 pre-alloyed steel powder 0.003 0.19 0.40 0.014 0.006
0.16 0.0005 <0.001 2.2 steel powder b-72 pre-alloyed steel
powder 0.005 0.20 0.38 0.013 0.004 0.16 0.0006 <0.001 2.5 b-73
pre-alloyed steel powder 0.004 0.20 0.38 0.012 0.004 0.16 0.0004
<0.001 3.2 b-74 pre-alloyed steel powder 0.003 0.18 0.39 0.012
0.004 0.16 0.0005 <0.001 4.6 b-75 pre-alloyed steel powder 0.004
0.20 0.39 0.013 0.005 0.16 0.0005 <0.001 8.1 b-81 composite
alloyed steel powder 0.004 0.20 0.39 0.014 0.005 0.18 0.0006
<0.001 6.0 b-82 composite alloyed steel powder 0.005 0.20 0.38
0.015 0.006 0.17 0.0005 <0.001 6.6 b-83 composite alloyed steel
powder 0.004 0.20 0.39 0.015 0.006 0.16 0.0005 <0.001 8.6 b-84
composite alloyed steel powder 0.005 0.18 0.39 0.016 0.005 0.16
0.0004 <0.001 12.4 b-85 composite alloyed steel powder 0.003
0.18 0.38 0.016 0.005 0.16 0.0005 <0.001 19.5 *The balance is Fe
and other inevitable impurities.
TABLE-US-00006 TABLE 6 Formulation of mixed powder for powder
metallurgy Evaluation result (a) Iron-based (b) Alloyed steel (c)
Cu (d) Graphite (e) Tensile powder powder powder powder Lubricant
Density strength Additon Additon Additon Additon Additon of of
amount amount Ratio amount amount amount fomed sintered *1 *1 of Mo
*1 *2 *2 *2 body body No. Type (mass %) Type (mass %) (mass %)
(mass %) (mass %) (mass %) (Mg/m.sup.3) (MPa) Category 39 a-5 0
b-71 100 2.2 2.0 0.7 0.5 6.85 607 Comparative example 40 10 b-72 90
2.3 2.0 0.7 0.5 6.94 635 Example 41 30 b-73 70 2.2 2.0 0.7 0.5 7.03
655 Example 42 50 b-74 50 2.3 2.0 0.7 0.5 7.08 643 Example 43 70
b-75 30 2.4 2.0 0.7 0.5 7.14 530 Comparative example 44 a-6 0 b-81
100 6.0 2.0 0.7 0.5 6.80 631 Comparative example 45 10 b-82 90 5.9
2.0 0.7 0.5 6.85 655 Example 46 30 b-83 70 6.0 2.0 0.7 0.5 6.92 678
Example 47 50 b-84 50 6.2 2.0 0.7 0.5 6.99 675 Example 48 70 b-85
30 5.9 2.0 0.7 0.5 7.05 573 Comparative example *1: Ratio to the
total of (a) iron-based powder and (b) alloyed steel powder. *2:
Ratio to the total of (a) iron-based powder, (b) alloyed steel
powder, (c) Cu powder, and (d) graphite powder.
* * * * *